The present invention relates to optical systems, and more particularly to a method and system for providing a dense wavelength division multiplexer.
To meet the increasing demand for information transmission capacity, multiple wavelength transmission is required. Dense wavelength division multiplexers (DWDMs) are used in optical systems for functions of combining or separating optical signals with densely packed wavelengths. A thin file filter (TFF) and a micro-optics based DWDM can fulfill such a requirement and usually provide good optical performance and environmental stability.
FIG. 1 depicts a conventional DWDM 10. The conventional DWDM 10 includes a filter 12 having a filter coating surface 14, a graduated index (GRIN) lens 16, a glass tube 18 holding a dual fiber capillary 20 with fibers 24 and 26 and a surrounding metal tube 22. The conventional DWDM 10 also includes a single fiber collimator 30 with a fiber 31. The fiber 24 provides an input optical signal, which is collimated by the GRIN lens 16 and provided to the filter 12, which transmits the optical signal with desired wavelength and reflects the remainder of the optical signal containing all other wavelengths. The single fiber collimator 30 receives the transmitted, filtered optical signal and couples this optical signal into fiber 31. The reflected optical signal is focused by GRIN lens 16 and coupled back to fiber 26. Thus, the conventional DWDM 10 can be used to separate out a portion, such as one or several wavelengths, of the optical signal input to the conventional DWDM 10.
Although the conventional DWDM 10 functions, one of ordinary skill in the art will readily recognize that the conventional DWDM has several drawbacks. First, the filter 12 is attached to the GRIN lens 16 at the filter coating surface 14. Typically, the filter 12 is attached to the GRIN lens 16 using UV epoxy 15 to form a filter/GRIN assembly, which is further attached with dual fiber capillary 20 using UV epoxy 17. Because the filter 12 is attached to the GRIN lens 16 at the filter coating surface, mechanical stress can be introduced into the coating by the epoxy curing process. As a result, the properties of the filter, such as the center wavelength, the bandwidth and the band shape are changed. Thus, these properties of the conventional DWDM 10 can be altered. This makes the conventional DWDM of less use in applications where the channel spacing is very narrow, such as 50 or 25 GHz. The conventional DWDM 10 is, therefore, not suitable for use with such densely packed optical signals.
In addition to being unable to be used for dense optical signals, the conventional DWDM 10 may also be unreliable in higher temperature and/or higher humidity environments. As discussed above, the filter 12 is affixed to the GRIN lens 16 using an UV epoxy 15. The assembly made from the GRIN lens 16/filter 12 and dual fiber capillary 20 are also affixed using UV epoxy 17. Such an epoxy is prone to softening in high temperature and/or high humidity environments. When the UV epoxy 15 and 17 softens, the dual fiber capillary 20, the GRIN lens 16 and filter 12 may move with respect to each other. As a result, the optical alignment critical to the functioning of the conventional DWDM 10 is compromised. Thus, the conventional DWDM 10 becomes unreliable in such environments.
Accordingly, what is needed is a system and method for providing a DWDM that is more reliable and suitable for dense optical signals. The present invention addresses such a need.
The present invention provides a method and system for providing a dense wavelength division multiplexer. The method and system include providing a dual fiber collimator, a filter and a filter holder. The dual fiber collimator includes a lens and a capillary. The capillary is for holding a plurality of fibers. The filter holder has an aperture therein. The filter is disposed between the dual fiber collimator and the filter holder. The filter has a first surface and a second surface opposite to the first surface. The first surface is covered with a filter coating. The filter is affixed to the filter holder by the second surface.
According to the system and method disclosed herein, the present invention provides a dens wavelength division multiplexer suitable for use with optical signals with densely packed wavelengths.